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diff --git a/fxjs/README b/fxjs/README new file mode 100644 index 0000000000..99d2f90bd8 --- /dev/null +++ b/fxjs/README @@ -0,0 +1,33 @@ +There are two separate wrappers for V8 here. One is called FXJS, and +it is used by the non-XFA code. The other is called FXJSE, and it is +used only by the XFA code. Additionally FXJSE may request services +from FXJS to bridge the two. + +Both the FXJS and FXJSE binding code needs to be replaced by something +saner, perhaps Gin or perhaps some IDL. See + https://bugs.chromium.org/p/pdfium/issues/detail?id=716 +for progress on the issue. + +FXJS binds objects by sticking a pointer to a CFXJS_PerObjectData in +the V8 object's internal slot. FXJSE binds objects by sticking a +pointer to either an actual v8 function object or a CFXJSE_HostObject +in the the V8 object's internal slot, depending upon whether the object +represents (in some notion) a "class" or an "instance". Also, V8 objects +bound in one library may unexpectedly arrive at the other given a script +that's trying to mess with us. + +To distinguish these cases, we use two internal slots for all bound +objects, regardless of the FXJS/FXJSE distinction. Slot 0 is the +tag and contains either: + kPerObjectDataTag for FXJS objects, or + g_FXJSETagString for FXJSE Host objects, or + One of 4 specific FXJSE_CLASS_DESCRIPTOR globals for FXJSE classes: + GlobalClassDescriptor + NormalClassDescriptor + VariablesClassDescriptor + formcalc_fm2js_descriptor + +Slot 1's contents are determined by these tags: + kPerObjectDataTag means to expect a CFXJS_PerObjectData. + g_FXJSETagString means to expect a CFXJSE_HostObject. + A FXJSE_CLASS_DESCRIPTOR pointer means to expect a v8 function. |